Release 0.4.0

• Changed NetMockResponse headers field's name
• Optimized code
• Improved doc and Readme

What's Changed

• Added code coverage and moved Resources out of core module by @DenisBronx in #7
• Js support core by @DenisBronx in #8
• • Updated Kdoc by @DenisBronx in #9
• Release/0.4.0 by @DenisBronx in #10

Full Changelog: 0.3.0...0.4.0